Plsql

1. 1
Agenda
 Summary of last class
 Loops

Simple Loops

WHILE Loops

FOR Loops
 Records
 Cursors

2. 2
Records
 User-defined composite types
 Provides a way to treat separate but logically related
variables as a unit
 Similar to “structures” in C
 Use the dot notation to refer to fields within a record
 v_StudentInfo.FirstName := ‘John’;
 In order to copy one record to another record, both records must
be of the same record type

3. 3
Records
 Syntax:
DECLARE
TYPE t_StudentRecord IS RECORD(
Student_ID NUMBER(5),
FirstName VARCHAR2(20),
LastName VARCHAR2(20) );
v_StudentInfo t_StudentRecord;
BEGIN
-- Process data here
EXCEPTION
-- Error handling would go here
END;
/
Use the dot notation to refer
to fields within a record.
Example:
v_StudentInfo.FirstName := ‘John’;

4. 4
Records
 To declare a record with the same
structure (i.e. fields & field types) as a
database row, use %ROWTYPE
 Syntax:
DECLARE
v_StudentInfo student%ROWTYPE;
BEGIN
-- Process data here
EXCEPTION
-- Error handling would go here
END;
/
NOTE:
Any NOT NULL constraints
that are defined for a column
within the table will not be
applicable to the declared
record when %ROWTYPE is
used.

5. 5
Cursors
 A pointer to the context area
 Context area contains:
 Number of rows processed by the statement
 A pointer to the parsed representation of the statement
 In the case of a query, the set of rows returned by the
query (i.e. the active set, active recordset)
 Follows standard declaration and scoping
 Naming Convention: c_CursorName
 Cursor Types:
 Explicit: user-defined
 Implicit: system-defined

6. 6
Explicit Cursors
 To use explicit cursors…
 Declare the cursor
 Open the cursor
 Fetch the results into PL/SQL variables
 Close the cursor

7. 7
Declaring Cursors
DECLARE
v_StudentID students.id%TYPE;
v_FirstName students.first_name%TYPE;
v_LastName students.last_name%TYPE;
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = ‘History’;
BEGIN
-- open cursor, fetch records & then close cursor here
END;
/

8. 8
OPEN Cursor
DECLARE
v_StudentID students.id%TYPE;
v_FirstName students.first_name%TYPE;
v_LastName students.last_name%TYPE;
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = ‘History’;
BEGIN
OPEN c_HistoryStudents;
-- fetch records & then close cursor here
END;
/

9. 9
FETCH Records
DECLARE
v_StudentID students.id%TYPE;
v_FirstName students.first_name%TYPE;
v_LastName students.last_name%TYPE;
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = ‘History’;
BEGIN
OPEN c_HistoryStudents;
LOOP
FETCH c_HistoryStudents INTO v_StudentID, v_FirstName, v_LastName;
EXIT WHEN c_HistoryStudents%NOTFOUND;
-- do something with the values that are now in the variables
END LOOP
-- close cursor here
END;/

10. 10
Close Cursor
DECLARE
v_StudentID students.id%TYPE;
v_FirstName students.first_name%TYPE;
v_LastName students.last_name%TYPE;
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = ‘History’;
BEGIN
OPEN c_HistoryStudents;
LOOP
FETCH c_HistoryStudents INTO v_StudentID, v_FirstName, v_LastName;
DBMS_OUTPUT.PUT_LINE(v_StudentID, v_FirstName, v_LastName);
EXIT WHEN c_HistoryStudents%NOTFOUND;
-- do something with the values that are now stored in the variables
END LOOP
CLOSE c_HistoryStudents;
END; /

11. 11
Cursor Attributes
 Cursors have four attributes…
 %FOUND

TRUE if the previous FETCH returned a row

Otherwise, FALSE
 %NOTFOUND

TRUE if the previous FETCH did NOT return a row

Otherwise, FALSE
 %ISOPEN

TRUE if the cursor is open,

Otherwise, FALSE
 %ROWCOUNT

Returns the # of rows that have been fetched by the cursor
so far

12. 12
Cursor Fetch Loop: WHILE Loop
DECLARE
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = 'History';
v_StudentData c_HistoryStudents%ROWTYPE;
BEGIN
OPEN c_HistoryStudents;
FETCH c_HistoryStudents INTO v_StudentData;
WHILE c_HistoryStudents%FOUND LOOP
INSERT INTO registered_students (student_id, department, course)
VALUES (v_StudentData.ID, 'HIS', 301);
INSERT INTO temp_table (num_col, char_col)
VALUES (v_StudentData.ID, v_StudentData.first_name || ' ' ||
v_StudentData.last_name);
FETCH c_HistoryStudents INTO v_StudentData;
END LOOP;
CLOSE c_HistoryStudents;
END;/

13. 13
Take Home Exercise #1
 Write an anonymous PL/SQL block that…
 Defines a cursor that points to a record set that contains
the sailors’ names, reservation date and boat id where
the boat color is red
 Opens the cursor
 Uses a simple loop to fetch each record in the active set
 Displays each last name, reservation date and boat id for
each record to the output screen
 Schema
Sailor (sid, sname, rating, age)
Boat (bid, bname, color)
Reservation(sid, bid, day)

14. 14
Cursor with Bind Variable(s)
DECLARE
v_StudentID students.id%TYPE;
v_FirstName students.first_name%TYPE;
v_LastName students.last_name%TYPE;
v_Major students.major%TYPE;
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = v_Major;
BEGIN
v_Major := ‘History’;
OPEN c_HistoryStudents;
LOOP
FETCH c_HistoryStudents INTO v_StudentID, v_FirstName, v_LastName;
EXIT WHEN c_HistoryStudents%NOTFOUND;
-- do something with the values that are now stored in the variables
END LOOP
CLOSE c_HistoryStudents;
END; /

15. 15
Bind Variables
 What are bind variables?
 Variables that are referenced in the cursor
declaration
 They must be declared BEFORE the cursor is
declared

i.e. variable must be declared before it can be used

The values of bind variables are examined ONLY
when the cursor is opened (at run time)

16. 16
Explicit Cursors with Bind
Variables
 To use explicit cursors with bind variables…
 Declare bind variables
 Then declare the cursor
 Assign values to bind variables
 Open the cursor
 Fetch the results into PL/SQL variables
 Close the cursor

17. 17
Take Home Exercise #2
 Modify your answer for Class Exercise #1
such that…
 It uses bind variables for color of boat instead
of hard-coding the values in the WHERE clause
 The FETCH is done inside of a WHILE loop
instead of inside of a simple loop.

18. 18
Implicit Cursors
 Used for INSERT, UPDATE, DELETE and SELECT…
INTO queries
 In SQL%NOTFOUND, SQL is called the implicit cursor
 PL/SQL opens & closes implicit cursors, which is also
called SQL cursor
 You don’t declare the implicit cursor
 If the WHERE clause fails…

For SELECT…INTO statement, then NO_DATA_FOUND error
is raised instead of SQL%NOTFOUND

For UPDATEs and DELETEs, SQL%NOTFOUND is set to
TRUE

19. 19
Example of Implicit Cursor
BEGIN
UPDATE rooms
SET number_seats = 100
WHERE room_id = 99980;
-- If the previous UPDATE statement didn't match any rows,
-- insert a new row into the rooms table.
IF SQL%NOTFOUND THEN
INSERT INTO rooms (room_id, number_seats)
VALUES (99980, 100);
END IF;
END;
/

20. 20
Example of Implicit Cursor
BEGIN
UPDATE rooms
SET number_seats = 100
WHERE room_id = 99980;
-- If the previous UPDATE statement didn't match any rows,
-- insert a new row into the rooms table.
IF SQL%ROWCOUNT = 0 THEN
INSERT INTO rooms (room_id, number_seats)
VALUES (99980, 100);
END IF;
END;

21. 21
-- Example of SELECT…INTO and NO_DATA_FOUND
set serveroutput on
DECLARE
-- Record to hold room information.
v_RoomData rooms%ROWTYPE;
BEGIN
-- Retrieve information about room ID -1.
SELECT *
INTO v_RoomData
FROM rooms
WHERE room_id = -1;
-- The following statement will never be executed, since
-- control passes immediately to the exception handler.
IF SQL%NOTFOUND THEN
DBMS_OUTPUT.PUT_LINE('SQL%NOTFOUND is true!');
END IF;
EXCEPTION
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE('NO_DATA_FOUND raised!');
END;
/

22. 22
SHOW ERRORS
 To display error message
 SQL> SHOW ERRORS;

23. 23
Summary of last class
 Cursors
 A pointer to the context area (active set)
 Name begins with c_
 Defined within the DECLARE section
 Types: Explicit vs. Implicit

Explicit: (1) Declare, (2) Open, (3) Fetch & (4) Close
 Bind variables

Variables that are referenced in the cursor declaration

Must be defined BEFORE the cursor

Values examined ONLY at run time
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = ‘History’;

24. 24
Take Home Exercise #1
DECLARE
CURSOR c_Reservations IS
SELECT s.sname, r.day, r.bid
FROM Sailor S, Reserve R, Boat B
WHERE R.sid = s.sid
AND R.bid = b.bid
AND B.color = ‘red’;
v_Reservation c_Reservations%ROWTYPE;
BEGIN
OPEN c_Reservations;
LOOP
FETCH c_Reservations INTO v_Reservation;
EXIT WHEN c_Reservations%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(v_Reservation.sname||’ ‘||v_Reservation.day||’
v_Reservation.bid);
END LOOP;
CLOSE c_Reservations;
END;/
Reserve
sid bid day
22 101 10/10/98
22 102 10/10/98
22 103 10/8/98
22 104 10/7/98
31 102 11/10/98
31 103 11/6/98
31 104 11/12/98
64 101 9/5/98
64 102 9/8/98
74 103 9/8/98
Boat
bid bname color
101 Interlake blue
102 Interlake red
103 Clipper green
104 Marine red
Sailor
sid sname rating age
22 Dustin 7 45.0
29 Brutus 1 33.0
31 Lubber 8 55.5
32 Andy 8 25.5
58 Rusty 10 35.0
64 Horatio 7 35.0
71 Zorba 10 16.0
74 Horatio 9 35.0
85 Art 3 25.5
95 Bob 3 63.5

25. 25
Cursor Attributes
 Cursors have four attributes…
 %FOUND

TRUE if the previous FETCH returned a row

Otherwise, FALSE
 %NOTFOUND

TRUE if the previous FETCH did NOT return a row

Otherwise, FALSE
 %ISOPEN

TRUE if the cursor is open,

Otherwise, FALSE
 %ROWCOUNT

Returns the # of rows that have been fetched by the cursor
so far

26. 26
Implicit Cursors
 Used for INSERT, UPDATE, DELETE and SELECT…
INTO queries
 In SQL%NOTFOUND, SQL is called the implicit cursor
 PL/SQL opens & closes implicit cursors, which is also
called SQL cursor
 You don’t declare the implicit cursor
 If the WHERE clause fails…

For SELECT…INTO statement, then NO_DATA_FOUND error
is raised instead of SQL%NOTFOUND

For UPDATEs and DELETEs, SQL%NOTFOUND is set to
TRUE

27. 27
Exceptions & Exception Handling
 What are exceptions & exception handlers?
 The method by which the program reacts & deals
with runtime errors
 How do they work?
 When a runtime error occurs, an exception is
raised
 Then control is passed to the exception handler
(i.e. the EXCEPTION section)
 Once control is passed to the exception handler,
there is no way to return to the executable section

28. 28
Declaring (Explicit) Exceptions
 How are explicit exceptions declared?
 Defined within the DECLARE section
 Defined using the keyword data type EXCEPTION
 Name starts with e_
Example:
DECLARE
e_TooManyStudents EXCEPTION;
v_CurrentStudents NUMBER(3);
v_MaxStudentsNUMBER(3);
BEGIN
-- process data here
EXCEPTION
-- handle exceptions here
END;/

29. 29
Raising Exceptions
 How are exceptions used?
 Within the executable section

Test a condition

If the condition evaluates to true, then use the
keyword RAISE to raise an exception

Can use the RAISE keyword with either predefined
exceptions or user-defined exceptions

30. 30
Raising Exceptions
DECLARE
e_TooManyStudents EXCEPTION;
v_CurrentStudents NUMBER(3);
v_MaxStudents NUMBER(3);
BEGIN
SELECT current_students, max_students
INTO v_CurrentStudents, v_MaxStudents
FROM classes
WHERE department = 'HIS' AND course = 101;
IF v_CurrentStudents > v_MaxStudents THEN
RAISE e_TooManyStudents;
END IF;
EXCEPTION
-- handle exceptions here
END;/

31. 31
Handling Exceptions
 Syntax
DECLARE
e_TooManyStudents EXCEPTION;
BEGIN
-- process data here
EXCEPTION
WHEN exception_Name1 THEN
statements;
WHEN exception_Name2 THEN
statements;
WHEN OTHERS THEN
statements;
END;/
 An exception can be handled by at most one
handler!

32. 32
Handling Exceptions
DECLARE
e_TooManyStudents EXCEPTION;
v_CurrentStudents NUMBER(3);
v_MaxStudents NUMBER(3);
BEGIN
SELECT current_students, max_students
INTO v_CurrentStudents, v_MaxStudents
FROM classes
WHERE department = 'HIS' AND course = 101;
IF v_CurrentStudents > v_MaxStudents THEN
RAISE e_TooManyStudents;
END IF;
EXCEPTION
WHEN e_TooManyStudents THEN
INSERT INTO log_table (info)
VALUES ('History 101 has ' || v_CurrentStudents ||
'students: max allowed is ' || v_MaxStudents);
WHEN OTHERS THEN
INSERT INTO log_table (info) VALUES ('Another error occurred');
END;/

33. 33
Handling Exceptions
 Built-in Functions

SQLCODE
 Returns the error code associated with the error
 Returns a value of 1 for user-defined exception
 Returns a value of 0 if no error with the last executed
statement

SQLERRM
 Returns the text of the error message
 Maximum length of an Oracle message is 512 characters
 Returns “User-defined Exception” for user-defined exception

RAISE_APPLICATION_ERROR
 RAISE_APPLICATION_ERROR(error#, error_message);
 Valid error #s: -20,000 and –20,999
 Error_Message MUST be less than 512 characters

34. 34
Key Concepts (thus far)
 PL/SQL Block
 IF-THEN-ELSE
 CASE
 Loops
 Simple Loops
 WHILE Loops
 FOR Loops
 Records
 Explicit
 Implicit
 Cursors
 Explicit
 Implicit
 Exception Handling
 Naming
Conventions

35. 35
Key Concepts: PL/SQL Block
 Basic building block/unit of PL/SQL programs

Three possible sections of a block

Declarative section (optional)

Executable section (required)
 Delimiters : BEGIN, END

Exception handling (optional)
 A block performs a logical unit of work in the
program
 Blocks can be nested

36. 36
Key Concepts: IF-THEN-ELSE &
CASE
IF boolean_expression1 THEN
sequence_of_statements;
[ELSIF boolean_expression2
THEN
sequence_of_statements]
[ELSE
sequence_of_statements]
END IF;
Either specify test case after CASE
keyword & OR specify test after
WHEN keyword
CASE
WHEN boolean_expression1 THEN
sequence_of_statements;
WHEN boolean_expression2 THEN
sequence_of_statements;
ELSE
sequence_of_statements;
END CASE;

37. 37
Key Concepts: PL/SQL Loops
 Used to execute a sequence of statements repeatedly
 When the number of iterations is unknown

Simple loops: executes at least once

WHILE loops: executes while the condition is true
 When the number of iterations is known in advance
 Numeric FOR Loops: executes a specific number of times
SIMPLE LOOP
LOOP
sequence_of_statements;
EXIT WHEN condition;
END LOOP;
WHILE LOOP
WHILE condition LOOP
sequence_of_statements;
END LOOP;
FOR LOOP
FOR loop_Counter IN IN [REVERSE] low..high
LOOP sequence_of_statements;
END LOOP;

38. 38
Key Concepts: Records
 Records
 Explicit

Name begins with t_

Once declared, can be used to declare other variables

TYPE t_StudentRecord IS RECORD(
Student_ID NUMBER(5),
FirstName VARCHAR2(20),
LastName VARCHAR2(20));
v_StudentInfo t_StudentRecord;
 Implicit

%ROWTYPE
 Declares a record with the same structure as
v_StudentInfo student%ROWTYPE
 Use dot notation to refer to fields within record

39. 39
Key Concepts: Cursors
 Cursors
 A pointer to the context area (active set)
 Name begins with c_
 Types: Explicit vs. Implicit

Explicit: (1) Declare, (2) Open, (3) Fetch & (4) Close
 Bind variables

Variables that are referenced in the cursor declaration

Must be defined BEFORE the cursor

Values examined ONLY at run time
CURSOR c_HistoryStudents IS
SELECT id, first_name, last_name
FROM students
WHERE major = ‘History’;

40. 40
Key Concepts: Cursors
 Explicit for SELECT statement
 Implicit for all other DML statements
 Used for INSERT, UPDATE, DELETE and SELECT…INTO queries
 PL/SQL opens & closes implicit cursors, which is called SQL
cursor
 If the WHERE clause fails…

For SELECT…INTO statement, then NO_DATA_FOUND error is
raised instead of SQL%NOTFOUND

For UPDATEs and DELETEs, SQL%NOTFOUND is set to TRUE
 Four attributes: %FOUND, %NOTFOUND, %ISOPEN,
%ROWCOUNT

41. 41
Key Concepts: Exceptions &
Exception Handling
 The method by which the program reacts & deals
with runtime errors
 When a runtime error occurs, an exception is
raised & control passes to the EXCEPTION section
 Once control is passed to the exception handler,
there is no way to return to the executable section
 User-defined exceptions
 Defined using the keyword data type EXCEPTION
 Use the keyword RAISE to raise an exception

42. 42
Key Concepts: Exceptions &
Exception Handling
 Pre-defined exceptions
 NO_DATA_FOUND

no data found in SELECT…INTO
 TOO_MANY_ROWS

SELECT…INTO produces more than one row
 INVALID_CURSOR

Cursor already closed
 CURSOR_ALREADY_OPEN

Cursor already open
 ZERO_DIVIDE

Division by zero
 INVALID_NUMBER

Data is not numeric
 (see book for others)

43. 43
Key Concepts: Exceptions &
Exception Handling
 Built-in Functions

SQLCODE
 Returns the error code associated with the error
 Returns a value of 1 for user-defined exception
 Returns a value of 0 if no error with the last executed statement

SQLERRM
 Returns the text of the error message
 Maximum length of an Oracle message is 512 characters
 Returns “User-defined Exception” for user-defined exception

RAISE_APPLICATION_ERROR
 RAISE_APPLICATION_ERROR(error#, error_message);
 Valid error #s: -20,000 and –20,999
 Error_Message MUST be less than 512 characters
 Used in procedures and functions

44. 44
Key Concepts: Exceptions &
Exception Handling
 Syntax
DECLARE
e_TooManyStudents EXCEPTION;
BEGIN
-- process data here
EXCEPTION
WHEN exception_Name1 THEN
statements;
WHEN exception_Name2 THEN
statements;
WHEN OTHERS THEN
statements;
END;/
 An exception can be handled by at most one handler!

45. 45
Key Concepts: Naming
Conventions
Item Naming Convention Note
primary keys *_pk * = tablename
*_fk1
*_fk2
*_fk#
*_u1 * = tablename
*_u2 * = tablename
*_u# # represents a sequential number
*_ck1 * = tablename
*_ck2 * = tablename
*_ck# # represents a sequential number
sequences *_sequence * = field name
script files *.sql * can be any name you choose
spooled files *.lst * can be any name you choose (e.g. TEST.LST)
cursors c_
exceptions e_
records t_ Explicit records
variables v_
foreign keys * = tablename; # = a sequential number
unique keys
checks

46. 46
SQL Statements
DML in PL / SQL
 The DML statements permitted are:
 Select
 Insert
 Update
 Delete

47. 47
DML in PL / SQL
Select
 SELECT statement in PL/SQL retrieves
data from a database table into:
 PL/SQL record
 set of PL/SQL variables
 Using SELECT in PL/SQL should only
return one row
 When you need to retrieve more than
one row from a table use a cursor

48. 48
DML in PL / SQL
Select Syntax
SELECT { * | select_list_item }
INTO { PL/SQL_record | variables}
FROM table_reference
WHERE where_clause
 each variable must be compatible with its
associated select list item
 count of variables must be same as
number of items in list
 record should contain fields that
correspond to the select list in type and
count

49. 49
select.sql
DECLARE
v_StudentRecord students%ROWTYPE;
v_Department classes.department%TYPE;
v_Course classes.course%TYPE;
BEGIN
SELECT *
INTO v_StudentRecord
FROM students
WHERE id = 10000;
SELECT department, course
INTO v_Department, v_Course
FROM classes
WHERE room_id = 99997;
END;

50. 50
DML in PL / SQL
Insert
 The INSERT statement inserts data into a
database table
 There are two variations of the INSERT
command
 add one row to a table using the specified
VALUES list
 add one or several rows when the insert
command uses a SELECT statement

51. 51
DML in PL / SQL
Insert Syntax
INSERT INTO table_reference
[(column_names)]
{VALUES (expression) | select_statement}
 use column names when the values

are listed in a different order than as defined
during table creation

Only a portion of the columns of the table
are used during insert
 table definition remains unchanged after
the new row is inserted

52. 52
DML in PL / SQL
Insert
 The word VALUES must precede the
list of data to be inserted
 Regarding the values in the list:
 a character string must be in single
quotes
 numbers can stand by themselves
 dates must be in single quotes

In the default Oracle date format

Converted using TO_DATE function (this is
the suggested method)

53. 53
Insert
Using Built-in Functions
 You can modify the contents of the values
before they are entered into a column of a
table
 by a VALUES list
 from a SELECT statement
 Use any of the built-in functions supported
by PL/SQL
 character
 date functions
 numeric
 conversion

54. 54
insert.sql
DECLARE
v_StudentID students.id%TYPE;
BEGIN
SELECT student_sequence.NEXTVAL
INTO v_StudentID
FROM dual;
INSERT INTO students (id, first_name, last_name)
VALUES (v_StudentID, 'Timothy', 'Taller');
INSERT INTO students (id, first_name, last_name)
VALUES (student_sequence.NEXTVAL, 'Patrick', 'Poll');
END;

55. 55
DML in PL / SQL
Insert with Select
 It is also possible to insert rows into a
table using the results of a SELECT
statement
 The results of a SELECT statement
 can return one or several rows based on
the WHERE clause
 can be a mix of columns from one or
more tables

56. 56
DML in PL / SQL
Update
 Requires setting specific values for
each column you wish to change
 Specifying which row or rows to
modify using a WHERE clause
 You can use built-in functions in
setting a value for the update

57. 57
Update in PL / SQL
Embedded SELECT
 It is possible to set values in an
UPDATE by embedding a SELECT
statement right in the middle of it
 SELECT has its own WHERE clause
 UPDATE has its own WHERE clause to
affect the rows
 You must be certain that the SELECT
will return no more than one row

58. 58
Embedded SELECT
BEGIN
UPDATE comfort set Midnight =
(SELECT temperature
FROM weather
WHERE city = ‘MANCHESTER’)
WHERE city = ‘WALPOLE’
AND SampleDate = TO_DATE (’22-DEC-1999’, ‘DD-MON-YYYY’);
END;

59. 59
DML in PL / SQL
Delete
 Removing a row or rows from a table
 WHERE clause is necessary to
removing only the rows you intend
 DELETE without the where clause will
delete all of the rows of a table

60. 60
delete.sql
DECLARE
v_StudentCutoff NUMBER;
BEGIN
v_StudentCutoff := 10;
DELETE FROM classes
WHERE current_students < v_StudentCutoff;
DELETE FROM students
WHERE current_credits = 0
AND major = 'Economics';
END;

61. 61
DML in PL / SQL
Truncate
 Another command for deleting records
from a table is the TRUNCATE command
TRUNCATE TABLE students;
 Does not operate the same as DELETE
 deletes all rows from a table
 cannot be rolled back
 records are unrecoverable
 does not run any DELETE triggers
 does not record any information in a snapshot
log

62. 62
DML in PL / SQL
WHERE Clause
 The SELECT, UPDATE, and DELETE
statements all include the WHERE clause
 Defines the active set (set of rows):
 returned by a SELECT query
 Acted upon by an UPDATE or DELETE
 Consists of conditions, joined together by
the boolean operators AND, OR, and NOT
 Conditions usually take the form of
comparisons using the relational operators
(such as: =, <>, >, >=, <, <=)

63. 63
DML in PL / SQL
WHERE Clause with Cursor
 The UPDATE, and DELETE statements
both include a WHERE clause with a
special syntax
 the WHERE CURRENT OF is used with a
cursor definition
 often processing done in a fetch loop
modifies the rows that have been
retrieved by a cursor

64. 64
DML in PL / SQL
WHERE Clause with Cursor
 This method consists of two parts:
 the FOR UPDATE clause in the cursor
declaration
 the WHERE CURRENT OF clause in an
UPDATE or DELETE statement

65. 65
forupdat.sql
DECLARE
v_NumCredits classes.num_credits%TYPE;
CURSOR c_RegisteredStudents IS
SELECT *
FROM students
WHERE id IN (SELECT student_id
FROM registered_students
WHERE department= 'HIS'
AND course = 101)
FOR UPDATE OF current_credits;

66. 66
forupdat.sql (cont.)
BEGIN
FOR v_StudentInfo IN c_RegisteredStudents LOOP
SELECT num_credits
INTO v_NumCredits
FROM classes
WHERE department = 'HIS'
AND course = 101;
UPDATE students
SET current_credits = current_credits + v_NumCredits
WHERE CURRENT OF c_RegisteredStudents;
END LOOP;
COMMIT;
END;

67. 67
DML in PL / SQL
Synonyms
 It is possible to create a synonym for
a:
 table
 view

sequence

stored

procedure

function

package

68. 68
DML in PL / SQL
Synonyms
 The syntax for creating a synonym is:
CREATE SYNONYM synonym_name FOR
reference;
 Where:
 synonym_name – name of your synonym
 reference – schema object being referenced

69. 69
Pseudocolums
Currval and Nextval
 CURRVAL and NEXTVAL are used with
sequences
 A sequence is an Oracle object used
to generate unique numbers
 Once created, you can access it with
its name by:
 sequence.CURRVAL
 sequence.NEXTVAL

70. 70
Pseudocolums
Currval and Nextval
 Sequence values can be used in:
 SELECT list of a query
 VALUES clause of an INSERT
 SET clause of an UPDATE
 Sequence values cannot be used in:
 WHERE clause
 PL/SQL statement